Over the last two decades, innovations in cement-based construction materials have led to improved durability, portability, modularity, and overall quality. For example, building blocks and panels made of a mixture of polystyrene foam, cement, and various chemical admixtures have come into wide use. These lightweight building blocks can be stacked or otherwise arranged during construction in the same general manner as ordinary cement blocks to form walls and other construction elements. These lightweight building blocks and panels can be shaped (e.g., by molding, cutting or drilling) and may include openings or channels to allow placement of reinforcing steel bars, concrete slurry, or other materials to increase the structural integrity and strength of completed construction elements.
Because these building blocks and panels contain a significant proportion of polystyrene foam, they are lighter and easier to handle during construction than pure cement blocks of similar size. Likewise, because of their composition, such blocks and panels are easy to cut, if desired, for installation of electrical wiring or plumbing or for other purposes. Such lightweight concrete blocks and panels have the additional advantage of being highly insulating when compared with traditional building materials. The R-value (a measure of thermal resistance used to characterize insulation) of such blocks and panels is much higher than that exhibited by buildings constructed of wood, brick, or other traditional building materials. Such blocks and panels are also highly fire and insect resistant, dramatically reducing the risk of fire or insect damage to structures made with them.
In a typical process for forming such blocks and panels, varying amounts of polystyrene foam and cement are mixed with liquid chemical admixtures to hold the foam granules together in a light-weight concrete mixture. The light-weight concrete mixture is poured into a mold and cured in the mold until it has hardened enough to be handled by people or machinery. The cured material is removed from the mold and cut to form smaller blocks or panels of desired sizes and shapes.
This typical process of curing a block in a mold has potential problems. The foam granules reduce the fluidity of the mixture and can create anomalies in the density (e.g., when constituent materials settle during curing) and shape (e.g., when the poured mixture does not fully occupy all the space within the mold) of the cured product. Thus, the density and dimensions of the cured, uncut block may be unpredictable. Cutting and re-shaping blocks after curing has several disadvantages, including the cost of wasted scrap material, the cost of personnel to make the required modifications to the block, and the time added to the manufacturing process to accommodate cutting or re-shaping steps.
Moreover, blocks that are cut after curing have an outer surface of open polystyrene granules. These open surfaces can easily absorb water. Thus, when individual building units are cut from larger pre-formed blocks, the individual building units typically must be coated with a water repellant material to prevent water absorption during or after construction.
Furthermore, the large molds used to create building blocks with the desired size, shape, and attributes for finished blocks and panels are heavy and difficult for equipment or workers to handle during the block manufacturing process.